This document summarizes several key organelles and structures within cells: - The Golgi apparatus stacks flattened sacs that modify and package proteins and lipids for secretion or transport within the cell. Lysosomes contain digestive enzymes and help break down materials through autophagy and phagocytosis. - Ribosomes are composed of RNA and proteins and are the site of protein synthesis. Chloroplasts contain chlorophyll and carry out photosynthesis through their thylakoid membranes and grana stacks in plant cells. - The cytoskeleton consists of microtubules, microfilaments, and intermediate filaments that give cells their shape and allow for cellular movement and transport.

1. Structure & Functions
of Organelles
bY SHALENI KAVIRAJAN
STPM BIOLOGY

2. GOLGI APPARATUS
 are stacks of flattened, hollow cavities enclosed by
membranes, which are often continuous with the
membranes of the ER
 usually located near to the nucleus & ER
 these stacks of flattened sacs / cavities are called
cisternae. Each sac in the organelle contains enzymes
that modify proteins
 Functions in modification, assembly, packaging,
storage and secretion of substances.
Golgi Apparatus

3.  Cis-end(convex) receives newly manufactured proteins
from ER, stores & modifies the proteins through
glycosylation & adds sugar molecules to form
glycoprotein.The modified proteins are then transported
into vesicles that bud off at the trans-end(concave) carrying
secretion of protein, glycoprotein / lipid. The contents are
released to the cell’s exterior by exocytosis.

4. LYSOSOMES
 special vesicles(spherical) which are formed by the Golgi
apparatus.
 The membrane(single layer of lipoprotein) is resistant to
digestion & prevents the release of enzymes which would
destroy the cell contents
 Contain high conc. of hydrolytic enzymes(ribonucleas,
deoxyribonucleas, carbohydrase, protease, lipase &
phosphatase) at pH value of 4 to 5(acidic)
 functions in : 1) cellular digestion 2) autophagy or
disposal of damaged cell/worn out components like
mitochondria 3) breakdown of a whole cell/autolysis (ex:
happens in the tail of tadpole where the digestion products
are used for building lungs & adult skin). For this reason,
they are sometimes called “suicide sacs.”

5.  are known to contain over 40 different enzymes that can
digest almost anything in the cell,including proteins,
RNA, DNA, and carbohydrates.
 also appear to perform other digestive processes, such as
those connected with phagocytosis and pinocytosis.
 Lysosomes also helps in destroying bacteria invasion

6. RIBOSOMES
 Found attached to the ER forming RER
 Occur singly or group together forming polysomes
 consist of rRna(produced in the nucleolus) and
proteins
 each ribosome is made of 2 non-identical subunits –
large & small (spheroid in shape)
 Provide site for synthesis of proteins(formation of
peptide bonds - amino acid are joined to form
polypeptide/protein)

7.  Ribosome Structure – Front View
 Large Subunit { Stalk, Centra Ridge, Wing}
 Small Subunit { Platform, Cleft,, Head}

8. CHLOROPLAST
 large plastids found only in the photosynthetic tissues of
plant cell
 these are the double-membrane bound organelles
 has a system of membranous flattened sacs(thylakoids)
stacked to form granum(where chlorophyll is located).
 site of photosynthesis

9.  Intergranal lamella connects one thylakoid of a granum to
another granum. The fluid outside the thylakoid is the stroma.
 It(grana & thylakoid membrane) provides large surface area
for chlorophyll & accessory pigments to be located – traps
light energy & carry out production of ATP & NADPH
 stroma – has enzymes to carry out light-independent
reaction(Calvin cycle) forming high energy organic
molecules such as ; sugar molecules

10. CYTOSKELETON
 The network of filamentous proteins structures
within the cell that determines the 3-D shape of animal
cells & give certain firmness in the plant cells
 The primary constituents of the cytoskeleton are
microtubules, microfilaments and intermediate
filaments

11. MICROTUBULES


12. MICROFILAMENT
 long, thin, contractile rods(6-7 nm in diameter) that
appear to be responsible for the movement of cells (both
external and internal movement).
 composed of one/two types of protein-actin(found in
skeletal muscles as thin filaments) & myosin(found in
skeletal muscles as thick filaments)

13.  Exists in bundles & found in layers in the cytoplasm
 dynamic - can change their length very
quickly(depends on their location & functions)
 Functions in:
i. assist in the cleavage process during cytokinesis
ii. role in cellular movements
Example: cytoplasmic streaming, cell motility –
phagocytosis & pinocytosis
iii. maintains cell shape

14. INTERMEDIATE FILAMENTS
